A vehicle may include a sensor for measuring vehicle speed. For example, automobile speed may be determined based on a rotating magnetic field that is generated by a magnet coupled to an axle or other part of the vehicle that moves proportionally to the vehicle speed. The vehicle speed may be communicated to an operator of the vehicle for assessing compliance with traffic control regulations (e.g., speed limits), or to a vehicle control system for automatically or otherwise controlling the vehicle based on the measured speed. If the sensor is damaged, however, such functionality may not be available.
In some transportation systems, government regulations require a vehicle, or certain designated classes or types of vehicles, to have redundant means for determining vehicle speed. For example, under some positive train control (PTC)-related regulations, locomotives or other powered rail vehicles may be required to have redundant speed sensors. Such redundant sensors, however, may add significantly to the cost of the locomotive or other rail vehicle.